Expression of NLRP3 inflammasome in the BSA-overloaded rats kidney

Objective To observe NLRP3 inflammasome expression and inflammatory cells infiltration in the BSA-overloaded rats kidney, and to investigate the potential mechanism of renal injury induced by proteinuria. Methods After unilateral right nephrectomy, eighteen healthy male Wistar rats were randomly divided into two groups: protein overload nephropathy model group (n=10), treated with intraperitoneal injections of bovine serum albumin (BSA); control group (n=8), treated with intraperitoneal injections of 0.9% saline for 9 weeks. Body weigh were measured every week and 24 h urine were collected in 0, 2, 5, 7, 9 week. The plasma levels of blood total protein (TP), albumin (Alb), serum creatinine (Scr) and blood urea nitrogen (BUN) were determined by automatic analyzers. Renal pathological changes were evaluated by PAS and Masson stains. Immunohistochemical staining was used to detect the expression of NLRP3, caspase-1, IL-1β, and IL-18, as well as the types of inflammatory cells. The NLRP3, caspase-1, IL-1β, and IL-18 protein and mRNA levels were also analyzed by Western blot and real-time PCR in two groups. Results It was found that there was a significant increase of proteinuria and BUN in model group compare to that in control group (all P＜0.05). However, there were no significant changes in body weight, TP, Alb and Scr between the two groups. Morphological study demonstrated that renal tubular epithelial cell injury, proteinaceous casts in tubular lumen, accompanying with the dominant macrophages and lymphocytes infiltration in interstitium in model group. The immunohistochemistry showed that there were more T (CD3+), B cells (CD20+) and macrophages (CD68+) in renal interstitium in model group than that in control group (P＜0.05). Tubulointerstitial injury score was higher than that of the control group (P＜0.05). Immunohistochemistry, Western blot and real-time PCR all showed that the expression of NLRP3, caspase-1, IL-18 and IL-1 β were significantly increased compared to those in control group (P＜0.05). Furthermore, there were significant correlations between proteinuria and IL-1β/IL-18 expression (P＜0.05). Conclusion NLRP3 inflammasome activation is involved in tubulointerstitial inflammation caused by proteinuria.